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sched/cache: Skip kernel threads for cache aware scheduling to rubustify the code

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Kernel thread should not be covered by cache aware scheduling as
it borrows the statistics from the user space thread. Filter the
kernel thread in account_mm_sched().

In theory a kernel thread does not have any valid
cache group, so !grp should gate the kernel thread.
Add the PF_KTHREAD check explicitly here for safety
reasons, to guard against future modifications and
to pair with task_tick_cache().

Fixes: df0d984759 ("sched/cache: Introduce infrastructure for cache-aware load balancing")
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: <stable@kernel.org> # 7.2.x
Link: https://patch.msgid.link/058f0c6ea7b991c177a17de347fa3157f25489a7.1790035273.git.tim.c.chen@linux.intel.com
This commit is contained in:
Chen Yu 2026-09-21 17:37:26 -07:00 committed by Ingo Molnar
parent b636fef85b
commit 65efcccddc
1 changed files with 7 additions and 1 deletions
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8
kernel/sched/fair.c
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@ -1907,8 +1907,14 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
/*
* init_task, kthreads and user thread created
* by user_mode_thread() don't have a cache group.
* In theory a kernel thread does not have any valid
* cache group, because sched_cache_fork() is not
* invoked for a kernel thread - !grp should gate the
* kernel thread. Use the PF_KTHREAD check explicitly
* here for safety reasons, to guard against future
* modifications and to pair with task_tick_cache().
*/
if (!grp || !grp->pcpu_sched)
if (p->flags & PF_KTHREAD || !grp || !grp->pcpu_sched)
return;
pcpu_sched = per_cpu_ptr(grp->pcpu_sched, cpu_of(rq));